Thursday, July 07, 2016

Six years ago the world woke up to the existence of an emerging antibiotic resistance gene dubbed New Delhi metallo-ß-lactamase-1, or NDM-1 (see NDM-1: A New Acronym To Memorize) which conveyed resistance to Carbapenums - drugs of last resort for treating difficult bacterial infections, including Escherichia coli (E. coli) and Klebsiella pneumoniae.

Since then, scattered variants of NDM-1 have begun to emerge around the globe, including NDM-2, NDM-4, NDM-5, NDM-7 and NDM-9.

Last November, in MCR-1: The Return Of The Plasmids,
we looked at the discovery of another resistance gene in China - dubbed mcr-1 - that conveys resistance to Colistin - essentially the last ditch drug available to treat many infections.

Given the rapid genetic diversification of the NDM resistance gene, I suppose we shouldn't be too surprised by this, but today the ECDC Journal Eurosurveillance reports on the first detection of a variant MCR gene, which they have dubbed mcr-2.

Follow the link to read the full report, after which I'll have a bit more.

We identified a novel plasmid-mediated colistin-resistance gene in porcine and bovine colistin-resistant Escherichia coli that did not contain mcr-1. The gene, termed mcr-2, a 1,617 bp phosphoethanolamine transferase harboured on an IncX4 plasmid, has 76.7% nucleotide identity to mcr-1. Prevalence of mcr-2 in porcine colistin-resistant E. coli (11/53) in Belgium was higher than that of mcr-1 (7/53). These data call for an immediate introduction of mcr-2 screening in ongoing molecular epidemiological surveillance of colistin-resistant Gram-negative pathogens.(Continue . . . )

Bacteria that carry the mcr-1 or mcr-2 genes aren't necessarily untreatable, since they may still be susceptible to other antibiotics, including Carbapenums.